This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPP third generation partnership project
BTS base transceiver station
BSC base station controller
BSS base station subsystem
CC call control
CS circuit switched
DL downlink (network towards UE)
FACCH fast associated control channel
FN frame number
GMSK Gaussian minimum shift keying
GSM global system for mobile communication
IE information element
Kc ciphering key
MM mobility management
MSC mobile switching center
RF radiofrequency
RRM radio resource management
SACCH slow associated control channel
SAPI service access point identifier
SI system information
TCH traffic channel
TDMA time division multiple access
UE user equipment
UL uplink (UE towards eNB)
In further refining the GSM radio access protocols, a security issue was recently identified concerning ciphering of text in System Information Type 5 (SI5) and Type 6 (SI6) messages, which are sent on the downlink SACCH. See for example documents GP-101242 (entitled “Alternating between different neighbour cell description formats, etc. by Vodafone) and GP-101243 (entitled “Additional A5/1-GEA1 Attack Countermeasures” by Vodafone) from the 3GPP TSG-GERAN Meeting #47 (Kunming, China; 30 Aug.-3 Sep. 2010). Those documents present potential solutions which are expected to be compatible with legacy mobile equipment already in use, but the inventors consider those proposed solutions as less than optimal. Document GP-101656 summarizing the 3GPP TSG-GERAN2 Meeting #47 (Kunming, China; 31 Aug.-2 Sep. 2010) shows that another solution is to not cipher at all on the SACCH. For reasons set forth below, the inventors also consider this proposal less than optimum.
These teachings set forth a solution to the above identified security gap which the inventors consider more robust and more flexible than the above referenced proposals.